USB powered tail light

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lionman   100 W

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USB powered tail light

Post by lionman » Jun 25 2018 9:35pm

I would like to have a tail light on my ebike that is powered directly off USB so that when I turn the bike on, the light comes on automatically so its always on.

There are quite a rechargeable lights but they only charge off USB so not really what I'm after.

I am installing a 60v to 5v USB converter which has 4 ports on it so it would be convenient to utilise a port on that.

Does anybody know of one?

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Re: USB powered tail light

Post by amberwolf » Jun 26 2018 12:47am

Don't know of one directly powered by USB, but you could take any 3xAA / 3xAAA powered light with a physical switch (rather than a "soft-off/on" button), and wire the USB cable from any old USB device to the battery contacts, in place of the batteries.

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Re: USB powered tail light

Post by lionman » Jun 26 2018 1:36am

Yeah was thinking that, even if it had a soft switch could probably bypass it pretty easily. LED circuits are pretty much the most basic there are, often just a resistor in series with the LEDs to limit current.

I could just buy any cheap one and rip the guts out and hot glue in my own little circuit. Much easier if there was a mass produced solution though.

There is the Supernova ones but they are a bit expensive for my tastes. Probably nice units though.
https://www.ebay.com.au/itm/Supernova-T ... SwhTBa59dr

I think dynamo lights are probably the closest thing? Although would still need to add a USB connector to the cable.

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Re: USB powered tail light

Post by lionman » Jul 12 2018 1:17am

still cant find anything that really suits.

Isn't it a bit strange that there are quite a few USB powered head lights, presumably to run of a USB power bank, but no tail lights at all on the market?

I'm thinking I might get a small USB powered head light and swap the white LEDs out for red ones.

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Re: USB powered tail light

Post by vagosofron » Jul 12 2018 6:24am

lionman wrote:
Jul 12 2018 1:17am
still cant find anything that really suits.

Isn't it a bit strange that there are quite a few USB powered head lights, presumably to run of a USB power bank, but no tail lights at all on the market?

I'm thinking I might get a small USB powered head light and swap the white LEDs out for red ones.
Or use a small red film to cover the glass and turn it into a taillight.

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Re: USB powered tail light

Post by minimum » Jul 12 2018 7:28am

vagosofron wrote:
Jul 12 2018 6:24am
Or use a small red film to cover the glass and turn it into a taillight.
Not a good idea as white LED emits very little in red spectrum (it's a blue led with phosphorous coating that converts part of the blue to yellow which in combination appears white to human eye).

When replacing white LED's to red, replace resistors accordingly as voltage drop is very different (~3,2V for white VS ~2V red).

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Re: USB powered tail light

Post by fechter » Jul 12 2018 8:11am

I had a tail light that was originally made for 2 AA alkaline batteries and converted it to 5v to run off a small dc-dc converter. I used a couple of diodes in series with the 5v to drop it closer to 3v. It had the issue with the power on switch needing to be pressed after power was applied. I solved the problem by placing a 0.1uF capacitor from 5v to the switch connection. The cap would start out at zero volts and was enough to trigger the button once when power was applied. If I bumped the power off/on quickly enough, it would change blinking modes.

On another one, the circuit blew up, so I took apart the light and replaced the electronic circuit with a dumb resistor so it just stays on steady. This is probably a lot simpler and more reliable, but you lose the flashing function.
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Re: USB powered tail light

Post by lionman » Jul 12 2018 8:29am

minimum wrote:
Jul 12 2018 7:28am

When replacing white LED's to red, replace resistors accordingly as voltage drop is very different (~3,2V for white VS ~2V red).
Or I assume I could use more LEDs in series?

I can put some of the knowledge gained from the hours of watching big Clive play with cheap LEDs to good use. Haha

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Re: USB powered tail light

Post by wturber » Jul 12 2018 9:53am

Why not just use a 12v adapter and 12v LED lights (or multi-voltage lights) that are commonly available at low prices. If you have a need for USB power as well, simply attach that to the 12v output. You can get 12v to USB adapters just about anywhere.

This is what I did on my bike. In fact, I added a 12v cigarette lighter/accessory plug and simply plug a USB adapter in to that for my phone and camera. When the adapter receives power, everything downstream comes on. Simple. Inexpensive.
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Re: USB powered tail light

Post by minimum » Jul 12 2018 12:40pm

lionman wrote:
Jul 12 2018 8:29am
Or I assume I could use more LEDs in series?
If string has 3 white LED's in series (with resistor) for 12V then 5 red LED's with the same resistor would be safe.
wturber wrote:
Jul 12 2018 9:53am
Why not just use a 12v adapter and 12v LED lights (or multi-voltage lights) that are commonly available at low prices.
Cheap low-powered LED lights are just at best case 3 LED's in series with resistor or at worst, 1 LED with big enough (480-520ohm) resistor to drop enough voltage for LED to survive (for a while).
For example, 1 white low power LED has Vd around 3,2V at 20mA, so LED consumes 3,2*0,02=0,064W
At 12VDC resistor has to drop 12-3,2=8,8V . Resistor value would be 8,8/0,02=440ohm (larger closest value preferred)
Resistor has to dissipate 8,8*0,02=0,176W . Thats 2,75 times more than LED itself.

Sure, it's quite common here to have 100000 times more power for motor but I find it waste of good electrons; no need to contribute to global warming :D

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Re: USB powered tail light

Post by Chalo » Jul 12 2018 1:04pm

lionman wrote:
Jun 25 2018 9:35pm
I would like to have a tail light on my ebike that is powered directly off USB so that when I turn the bike on, the light comes on automatically so its always on.

There are quite a rechargeable lights but they only charge off USB so not really what I'm after.

I am installing a 60v to 5v USB converter which has 4 ports on it so it would be convenient to utilise a port on that.

Does anybody know of one?
Pretty much any LED tail light for a bicycle generator should work well with 5VDC from a USB port. They are nominally designed for 6VAC, but they usually are quite versatile in terms of the voltage required to light them (which varies with the speed of a bicycle generator). It's only a matter of wiring it to the plug.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

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Re: USB powered tail light

Post by arthurtuxedo » Jul 12 2018 1:17pm

I bought one from Lunacycle that can run off any voltage from 12-60 V. I wired it directly from the ignition switch (which comes straight off the 36V battery) with no need to step down the volts. It looks like they don't sell that one anymore, but I'm sure you can find similar ones on eBay or Alibaba.

For me it was important to have a permanently wired light that would be on the bike at all times so I could never forget it or be caught without it, but that wouldn't be a tempting target for thieves who would find it useless without a soldering iron or crimper.

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Re: USB powered tail light

Post by wturber » Jul 12 2018 1:41pm

minimum wrote:
Jul 12 2018 12:40pm

For example, 1 white low power LED has Vd around 3,2V at 20mA, so LED consumes 3,2*0,02=0,064W
At 12VDC resistor has to drop 12-3,2=8,8V . Resistor value would be 8,8/0,02=440ohm (larger closest value preferred)
Resistor has to dissipate 8,8*0,02=0,176W . Thats 2,75 times more than LED itself.

Sure, it's quite common here to have 100000 times more power for motor but I find it waste of good electrons; no need to contribute to global warming :D
All of the LED devices I use have multiple LED. So I'm betting the resistor loss pretty low. Of all the ways I might be wasting electrons, bike LED resistor loss is way down on the list.
"Commuter - DC Booster"
Iron Horse 3.0 hardtail - 48V / 1000W / 470rpm generic Chinese DD Hub motor (ebay)
8 x 36v 4.3ah 10s 2P battery packs - 1500W 30A DC Boost Converter delivers 54v and about 1000 watts peak
53T/42T Sakae Road cranks - 30mph+ on flats
viewtopic.php?f=2&t=90369

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Re: USB powered tail light

Post by fechter » Jul 13 2018 8:31am

I didn't find any on eBay except ones with license plate holders for scooters.

The Luna one shows here, but couldn't tell if they have stock
https://lunacycle.com/black-friday/rear-light/

And a couple of choices from Grin:
http://www.ebikes.ca/shop/electric-bicy ... ights.html
One of them is listed for $15.
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Re: USB powered tail light

Post by lionman » Jul 13 2018 11:13pm

fechter wrote:
Jul 13 2018 8:31am
I didn't find any on eBay except ones with license plate holders for scooters.

The Luna one shows here, but couldn't tell if they have stock
https://lunacycle.com/black-friday/rear-light/

And a couple of choices from Grin:
http://www.ebikes.ca/shop/electric-bicy ... ights.html
One of them is listed for $15.
Thanks for providing some links. Unfortunately I'm in Australia and most things shipped from North America have ridiculous shipping costs.

That grin light is $15, plus $41 shipping!

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Re: USB powered tail light

Post by wturber » Jul 13 2018 11:47pm

fechter wrote:
Jul 13 2018 8:31am
I didn't find any on eBay except ones with license plate holders for scooters.
For taillights, I use red LED strips. For a headlight I use this light:

https://www.amazon.com/Wisamic-Projecti ... 3Z7T0586H9

There are many bright 12 volt Multi-LED red lights and bulbs on Amazon and ebay Australia. These are made mostly for cars, trailers and so forth, not bicycles. I'm pretty easy to spot - day or night.
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"Commuter - DC Booster"
Iron Horse 3.0 hardtail - 48V / 1000W / 470rpm generic Chinese DD Hub motor (ebay)
8 x 36v 4.3ah 10s 2P battery packs - 1500W 30A DC Boost Converter delivers 54v and about 1000 watts peak
53T/42T Sakae Road cranks - 30mph+ on flats
viewtopic.php?f=2&t=90369

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